One-pot synthesis of optically active allyl esters via lipase-vanadium combo catalysis

The combination of vanadium-oxo compounds (3 or 4) with a lipase produced the regio- and enantioconvergent transformation of racemic allyl alcohols (1 or 2) into optically active allyl esters. In this system, the vanadium compounds catalyzed the continuous racemization of the alcohols along with the transposition of the hydroxyl group, while the lipase effected the chemo- and enantioselective esterification to achieve the dynamic kinetic resolution.     

Extensions between finite-dimensional simple modules over a generalized current Lie algebra

We calculate the first extension groups for finite-dimensional simple modules over an arbitrary generalized current Lie algebra, which includes the case of loop Lie algebras and their multivariable analogs.     

Fluorophotometric Determination of Hydrogen Peroxide with Fluorescin in the Presence of Cobalt (II) and Reaction Against Other Reactive Oxygen Species

A fluorophotometric method for the determination of hydrogen peroxide (H₂O₂) using fluorescin was developed. This method was based on the oxidative reaction of fluorescin, a colorless, non-fluorescent lactoid fluorescein, by H₂O₂ to give highly fluorescein fluorescence emission. In the determination of H₂O₂, the calibration curve exhibited linearity over the H₂O₂ concentration range of 1.5–310 ng mL⁻¹ at an emission wavelength of 525 nm with an excitation of 500 nm and with relative standard deviations (n = 6) of 2.51%, 2.48%, and 1.31% for 3.1 ng mL⁻¹, 30.8 ng mL⁻¹, and for 308 ng mL⁻¹ of H₂O₂, respectively. The detection limit for H₂O₂ was 1.9 ng mL⁻¹ six blank determinations was performed (ρ = 6). This proposed method was applied to detection of other reactive oxygen species and nitrogen species (ROS/RNS) such as singlet oxygen (¹O₂), hydroxyl radical (^•OH), peroxynitrite (ONOO⁻) etc., and it was possible to detect them with a high sensitivity. In addition, this proposed method was applied to the recovery tests of H₂O₂ in calf serum, human saliva, rain water, and wheat noodles; the results were satisfactory.     

Dissociation processes of Kr2(+) and Kr3(+) studied by threshold photoelectron-photoion coincidence measurements

A time-of-flight (TOF) ion mass spectrum in coincidence with threshold photoelectrons was measured in the photon energy region between the first and second dissociation limits of Kr2(+) to examine the decay processes of the Kr2(+) II(1/2u) state. The measured TOF spectrum reveals that Kr+ fragment ions are produced through dissociation of the repulsive I(1/2g) state, which can be formed by the decay process of the II(1/2u) state accompanied with emission of photons. The potential-energy curve of the I(1/2g) state is deduced with detailed analysis of the observed TOF spectrum, in which the radiative lifetime of the II(1/2u) state was also derived to be 2.5 micros. Additionally, evidence of the dissociation process of Kr3(+) ions was obtained in the same photon energy region, where the dominant channel is Kr3(+) --> Kr2(+) + Kr.     

Short communication: An alternative and effective catalyst for the silastannation of arylacetylenes with Me3SiSnBu3 at room temperature

The palladium‐catalyzed silastannation of acetylenes with tributyl(trimethylsilyl)stannane in the presence of triethylphosphite is reported for the first time. The reaction occurs at room temperature to give (Z)‐silyl(stannyl)ethenes in high yields. The protodemetallation of the resulting adducts with HCl–tetraethylammonium chloride is described first, which demonstrates that the reaction is governed only by the stability of a carbonium ion arising from the protonation to (Z)‐silyl(stannyl)ethenes rather than the hard and soft acid and base principle, i.e. the β‐cation stabilization effect (σ–π stabilization one) of a stannyl group in the carbonium ion is rather significant. Copyright © 2004 John Wiley & Sons, Ltd.     

Nickel-catalyzed reductive cleavage of aryl alkyl ethers to arenes in absence of external reductant

The reductive cleavage of the C–O bonds of aryl ethers has great potential in organic synthesis. Although several catalysts that can promote the reductive cleavage of aryl ethers have been reported, all such systems require the use of an external reductant, e.g., hydrosilane or hydrogen. Here, we report the development of a new nickel-based catalytic system that can cleave the C–O bonds of ethers in the absence of an external reductant. The hydrogen atom required in this new reductive cleavage reaction is provided by the alkoxy group of the substrate, which serves as an internal reductant. The absence of an external reductant enables the unique chemoselectivity, i.e., the selective reduction of an alkoxy group over alkenes and ketones.     

Total synthesis of kehokorins A and B

The total synthesis of a dibenzofuran rhamnoside, kehokorin A, and its aglycone, kehokorin B, was achieved via a route including Suzuki-Miyaura cross-coupling followed by Ullmann ether synthesis to form a dibenzofuran, stepwise bromination at C7 of the dibenzofuran, a second Suzuki-Miyaura cross-coupling to install a 4-methoxyphenyl group at C7, and rhamnosylation.